Membranes of polyurethane based materials including polyester polyols

ABSTRACT

The present invention relates to membranes including an urethane including a polyester polyol, wherein the membrane has a gas transmission rate of 15.0 or less for nitrogen gas wherein the membrane has an average thickness of approximately 20.0 mils. Under certain embodiments, the membranes include blends of one or more polyester polyol based thermoplastic urethanes and one or more barrier materials. The membranes can be employed in a variety of applications and can be used as either monolayers or multi-layered laminates.

This is a continuation of U.S. patent application Ser. No. 08/571,160,filed Dec. 12, 1995, now U.S. Pat. No. 6,013,340, which is acontinuation-in-part of U.S. patent application Ser. No. 08/475,275,filed Jun. 7, 1995.

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 08/475,275 abandoned, entitled “Membranes IncludingA Barrier Layer Employing Polyester Polyols,” filed on Jun. 7, 1995,which is hereby expressly incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to membranes and, more particularly, tomembranes which, under certain embodiments, serve to selectively controlthe diffusion of gases through the membrane. Additionally, the membranenot only selectively controls the diffusion of gases through themembrane, but also allows for the controlled diffusion of gases normallycontained in the atmosphere.

BACKGROUND OF THE INVENTION

Membranes, and more particularly, membranes useful for containingfluids, including liquids and/or gases, in a controlled manner, havebeen employed for years in a wide variety of products ranging frombladders useful in inflatable objects, including vehicle tires andsporting goods for example; to accumulators used on heavy machinery; tocushioning devices useful in footwear. Regardless of the intended use,membranes must generally be flexible, resistant to environmentaldegradation and exhibit excellent gas transmission controls. Often,however, materials which exhibit acceptable flexibility characteristicstend to have an unacceptably low level of resistance to gas permeation.In contrast, materials which exhibit an acceptable level of resistanceto gas permeation tend to have an unacceptably low level of flexibility.

In an attempt to address the concerns of both flexibility andimperviousness to gases, U.S. Pat. No. 5,036,110 which issued Jun. 30,1991, to Moreaux describes resilient membranes for fittinghydropneumatic accumulators. According to Moreaux '110, the membranedisclosed consists of a film formed from a graft polymer which is thereaction product of an aromatic thermoplastic polyurethane with acopolymer of ethylene and vinyl alcohol, with this film being sandwichedbetween layers of thermoplastic polyurethane to form a laminate. WhileMoreaux '110 attempts to address the concerns in the art relating toflexibility and imperviousness to gases, a perceived drawback of Moreauxis that the film described is not processable utilizing conventionaltechniques such as sheet extrusion, for example. Thus, the presentinvention is directed to membranes which are flexible, have goodresistance to gas transmission, and under certain embodiments areprocessable into laminates utilizing conventional techniques such assheet extrusion which are highly resistant to delamination.

While it should be understood by those skilled in the art upon review ofthe following specification and claims that the membranes of the presentinvention have a broad range of applications, including but not limitedto bladders for inflatable objects such as footballs, basketballs,soccer balls, inner tubes; substantially rigid flotation devices such asboat hulls; flexible floatation devices such as tubes or rafts; as acomponent of medical equipment such as catheter balloons; fuel lines andfuel storage tanks; various cushioning devices such as thoseincorporated as part of an article of footwear or clothing; as part ofan article of furniture such as chairs and seats, as part of a bicycleor saddle, as part of protective equipment including shin guards andhelmets; as a supporting element for articles of furniture and, moreparticularly, lumbar supports; as part of a prosthetic or orthopedicdevice; as a portion of a vehicle tire and particularly, the outer layerof the tire, as well as being incorporated as part of certain recreationequipment such as components of wheels for in-line or roller skates, toname a few, still other applications are possible. For example, onehighly desirable application for the membranes of the present inventioninclude their use in forming accumulators which are operable under highpressure environments such as hydraulic accumulators as will bediscussed in greater detail below.

For convenience, but without limitation, the membranes of the presentinvention will hereinafter generally be described in terms of eitheraccumulators or in terms of still another highly desirable application,namely for cushioning devices used in footwear. In order to fullydiscuss the applicability of the membranes in terms of cushioningdevices for footwear, a description of footwear in general is believedto be necessary.

Footwear, or more precisely, shoes generally include two majorcategories of components namely, a shoe upper and the sole. The generalpurpose of the shoe upper is to snugly and comfortably enclose the foot.Ideally, the shoe upper should be made from an attractive, highlydurable, yet comfortable material or combination of materials. The sole,which also can be made from one or more durable materials, isparticularly designed to provide traction and protect the wearer's feetand body during use. The considerable forces generated during athleticactivities require that the sole of an athletic shoe provide enhancedprotection and shock absorption for the feet, ankles and legs of thewearer. For example, impacts which occur during running activities cangenerate forces of up to 2-3 times the body weight of an individualwhile certain other activities such as, for example, playing basketballhave been known to generate forces of up to approximately 6-10 times anindividual's body weight. Accordingly, many shoes and, moreparticularly, many athletic shoes are now provided with some type ofresilient, shock-absorbent material or shock-absorbent components tocushion the user during strenuous athletic activity. Such resilient,shock-absorbent materials or components have now commonly come to bereferred to in the shoe manufacturing industry as the midsole.

It has therefore been a focus of the industry to seek midsole designswhich achieve an effective impact response in which both adequate shockabsorption and resiliency are appropriately taken into account. Suchresilient, shock-absorbent materials or components could also be appliedto the insole portion of the shoe, which is generally defined as theportion of the shoe upper directly underlining the plantar surface ofthe foot.

A particular focus in the footwear manufacturing industry has been toseek midsole or insert structure designs which are adapted to containfluids, in either the liquid or gaseous state, or both. Examples ofgas-filled structures which are utilized within the soles of shoes areshown in U.S. Pat. No. 900,867 entitled “Cushion for Footwear” whichissued Oct. 13, 1908, to Miller; U.S. Pat No. 1,069,001 entitled“Cushioned Sole and Heel for Shoes” which issued Jul. 29, 1913, to Guy;U.S. Pat. No. 1,304,915 entitled “Pneumatic Insole” which issued May 27,1919, to Spinney; U.S. Pat. No. 1,514,468 entitled “Arch Cushion” whichissued Nov. 4, 1924, to Schopf; U.S. Pat. No. 2,080,469 entitled“Pneumatic Foot Support ” which issued May 18, 1937, to Gilbert; U.S.Pat. No. 2,645,865 entitled “Cushioning Insole for Shoes” which issuedJul. 21, 1953, to Towne; U.S. Pat. No. 2,677,906 entitled “CushionedInner Sole for Shoes and Method of Making the Same” which issued May 11,1954, to Reed; U.S. Pat. No. 4,183,156 entitled “Insole Construction forArticles of Footwear” which issued Jan. 15, 1980, to Rudy; U.S. Pat. No.4,219,945 entitled “Footwear” which issued Sep. 2, 1980, also to Rudy;U.S. Pat. No. 4,722,131 entitled “Air Cushion Shoe Sole” which issuedFeb. 2, 1988, to Huang; and U.S. Pat. No. 4,864,738 entitled “SoleConstruction for Footwear” which issued Sep. 12, 1989, to Horovitz. Aswill be recognized by those skilled in the art, such gas filledstructures often referred to in the shoe manufacturing industry as“bladders” typically fall into two broad categories, namely (1)“permanently” inflated systems such as those disclosed in U.S. Pat. Nos.4,183,156 and 4,219,945 and (2) pump and valve adjustable systems asexemplified by U.S. Pat. No. 4,722,131. By way of further example,athletic shoes of the type disclosed in U.S. Pat. No. 4,182,156 whichinclude “permanently” inflated bladders have been successfully soldunder the trade mark “Air-Sole” and other trademarks by Nike, Inc. ofBeaverton, Oreg. To date, millions of pairs of athletic shoes of thistype have been sold in the United States and throughout the world.

The permanently inflated bladders have historically been constructedunder methods using a flexible thermoplastic material which is inflatedwith a large molecule, low solubility coefficient gas otherwise referredto in the industry as a “super gas.” By way of example, U.S. Pat. No.4,340,626 entitled “Diffusion Pumping Apparatus Self-Inflating Device”which issued Jul. 20, 1982, to Rudy, which is expressly incorporatedherein by reference, discloses selectively permeable sheets of filmwhich are formed into a bladder and thereafter inflated with a gas ormixture of gases to a prescribed pressure which preferably is aboveatmospheric pressure. The gas or gases utilized ideally have arelatively low diffusion rate through the selectively permeable bladderto the exterior environment while gases such as nitrogen, oxygen andargon which are contained in the atmosphere and have a relatively highdiffusion rate are able to penetrate the bladder. This produces anincrease in the total pressure within the bladder, by the addition ofthe partial pressures of the nitrogen, oxygen and argon from theatmosphere to the partial pressures of the gas or gases containedinitially injected into the bladder upon inflation. This concept of arelative one-way addition of gases to enhance the total pressure of thebladder is now known as “diffusion pumping.”

With regard to the systems utilized within the footwear manufacturingindustry prior to and shortly after the introduction of the Air-Sole™athletic shoes, many of the midsole bladders consisted of a single layergas barrier type films made from polyvinylidene chloride based materialssuch as Saran® (which is a registered trademark of the Dow Chemical Co.)and which by their nature are rigid plastics, having relatively poorflex fatigue, heat sealability and elasticity.

Still further, bladder films made under techniques such as laminationsand coatings which involve one or more barrier materials in combinationwith a flexible bladder material (such as various thermoplastics) canpotentially present a wide variety of problems to solve. Suchdifficulties with composite constructions include layer separation,peeling, gas diffusion or capillary action at weld interfaces, lowelongation which leads to wrinkling of the inflated product, cloudyappearing finished bladders, reduced puncture resistance and tearstrength, resistance to formation via blow-molding and/or heat-sealingand RF welding, high cost processing, and difficulty with foamencapsulation and adhesive bonding, among others.

Yet another issue with previously known multi-layer bladders is the useof tie-layers or adhesives in preparing laminates. The use of such tielayers or adhesives generally prevent regrinding and recycling of anywaste materials created during product formation back into an usableproduct, and thus, also contribute to high cost of manufacturing andrelative waste. These and other perceived short comings of the prior artare described in more extensive detail in U.S. Pat. Nos. 4,340,626;4,936,029 and 5,042,176, all of which are hereby expressly incorporatedby reference.

Previously known multi-layer bladders which specifically eliminateadhesive tie layers have been known to separate or de-laminateespecially along seams and edges. Thus, it has been a relatively recentfocus of the industry to develop laminated bladders which reduce oreliminate the occurrence of delamination ideally without the use of a“tie layer.” In this regard, the cushioning devices disclosed inco-pending U.S. application Ser. Nos. 08/299,286 and 08/299,287eliminate adhesive tie layers by providing membranes including a firstlayer of thermoplastic urethane and a second layer including a barriermaterial such as a copolymer of ethylene and vinyl alcohol whereinhydrogen bonding occurs over a segment of the membranes between thefirst and second layers. While the membranes disclosed in U.S. patentapplication Ser. No. 08/299,287 and the laminated flexible membranes ofU. S. patent application Ser. No. 08/299,286 are believed to offer asignificant improvement in the art, still further improvements areoffered according to the teachings of the present invention.

With the extensive commercial success of the products such as theAir-Sole™ shoes, consumers have been able to enjoy products with a longservice life, superior shock absorbency and resiliency, reasonable cost,and inflation stability, without having to resort to pumps and valves.Thus, in light of the significant commercial acceptance and success thathas been achieved through the use of long life inflated gas filledbladders, it is highly desirable to develop advancements relating tosuch products. One goal then is to provide flexible, “permanently”inflated, gas-filled shoe cushioning components which meet, andhopefully exceed, performance achieved by such products as the Air-Soleυathletic shoes offered by Nike, Inc.

An accepted method of measuring the relative permeance, permeability anddiffusion of different film materials is set forth in the proceduredesignated as ASTM D-1434-82-V. According to ASTM D-1434-82-V,permeance, permeability and diffusion are measured by the followingformulas: $\underset{\_}{Permeance}$ $\begin{matrix}{\frac{\left( {{quantity}\quad {of}\quad {gas}} \right)}{({area}) \times ({time}) \times \left( {{press}.\quad {diff}.} \right)} = \begin{matrix}{Permeance} \\{({GTR})/\left( {{press}.\quad {diff}.} \right)}\end{matrix}} \\{= \frac{{cc}.}{\left( {{sq}.m} \right)\quad \left( {24{hr}} \right)\quad ({Pa})}}\end{matrix}$ $\underset{\_}{Permeability}$ $\begin{matrix}{\frac{\left( {{quantity}\quad {of}\quad {gas}} \right) \times \left( {{film}\quad {thick}} \right)}{\left. {({area}) \times ({time}) \times {{press}.\quad {diff}.}} \right)} = \begin{matrix}{Permeability} \\{({GTR}) \times {\left( {{film}\quad {thick}} \right)/\left( {{press}.\quad {diff}.} \right)}}\end{matrix}} \\{= \frac{({cc})({mil})}{\left( {{sq}.m} \right)\quad \left( {24{hr}} \right)\quad ({Pa})}}\end{matrix}$ $\underset{\_}{Diffusion}$$\frac{\left( {{quantity}\quad {of}\quad {gas}} \right)}{({area}) \times ({time})} = {\begin{matrix}{{Gas}\quad {Transmission}\quad {Rate}} \\({GTR})\end{matrix} = \frac{cc}{\left( {{sq}.m} \right)\left( {24{hr}} \right)}}$

By utilizing the above listed formulas, the gas transmission rate incombination with a constant pressure differential and the film'sthickness, can be utilized to define the movement of gas under specificconditions. In this regard, the preferred gas transmission rate (GTR)for a membrane having an average thickness of approximately 20.0 milssuch as those useful for forming a cushioning device used as a shoecomponent which seeks to meet the rigorous demands of fatigue resistanceimposed by heavy and repeated impacts will preferably have a gastransmission rate (GTR) of 15.0 or less for nitrogen gas according toASTM D-1434-82-V. More preferably, the membranes will have a GTR of lessthan about 2.0 at an average thickness of 20 mils.

It is, therefore, one object of the present invention to providemembranes including both single layer and multi-layer constructionswhich offer enhanced flexibility, durability and resistance to theundesired transmission of fluids therethrough.

It is another object of the present invention to provide membranes whichcan be inflated with a gas such as nitrogen wherein the membraneprovides for a gas transmission rate value of 15.0 or less, based on a20 mils average thickness.

It is still another object of the present invention to providemembranes, particularly those employed as cushioning devices, having arelatively high degree of transparency.

It is another object of the present invention to provide monolayermembranes which are readily processable into various products.

It is yet another object of the present invention to provide monolayermembranes and, under certain applications, multilayer membranes whichare reprocessable and repairable.

It is yet another object of the present invention to provide membraneswhich can be formed into laminated objects such as cushioning devices oraccumulators, among others, which better resist delamination and alsomay not require a tie layer between the layers.

It is a further object of the present invention to provide membraneswhich are formable utilizing various techniques including, but notlimited to, blow-molding, tubing, sheet extrusion, vacuum-forming,heat-sealing, casting, liquid casting, low pressure casting, spincasting, reaction injection molding and RF welding.

Still another object of the present invention is to provide membraneswhich prevent gas from escaping along interfaces between the layers inlaminated embodiments and particularly along seems via capillary action.

It is yet another object of the present invention to provide a membranewhich allows for footwear processing such as encapsulation of a membranewithin a formable material.

While the aforementioned objects provide guidance as to possibleapplications and advantages for the membranes of the present invention,it should be recognized by those skilled in the art that the recitedobjects are not intended to be exhaustive or limiting.

SUMMARY OF THE INVENTION

To achieve the foregoing objects, the present invention providesmembranes which preferably have one or more of the following: (1) adesirable level of flexibility (or rigidity); (2) a desirable level ofresistance to degradation caused by moisture; (3) an acceptable level ofimperviousness to fluids which can be in the form of gases, liquids orboth depending mainly on the intended use of the product; and (4)resistance to delamination when employed in a multi-layer structure.Regardless of the membrane embodiment, each membrane in accordance withthe teachings of the present invention includes a layer comprised of apolyester polyol based polyurethane. The aforementioned layer may alsoinclude at least one barrier material selected from the group consistingof co-polymers of ethylene and vinyl alcohol, polyvinylidene chloride,co-polymers of acrylonitrile and methyl acrylate, polyethyleneterephthalate, aliphatic and aromatic polyamides, crystalline polymersand polyurethane engineering thermoplastics blended with thepolyurethane prior to forming the membranes.

The polyester polyol based urethanes employed, if not commerciallyavailable, are preferably formed as the reaction product of (a) one ormore carboxylic acids having six or less carbon atoms with one or morediols having six or less carbon atoms; (b) at least one isocyanateand/or diisocyanate; and (c) optionally, but preferably, one or moreextenders. The polyester polyol may also include a relatively smallamount of one or more polyfunctional materials such as triols which areincluded as part of the reaction product. In addition to the foregoing,the polyester polyol based urethanes may optionally employ one or moreof the following: (d) hydrolytic stabilizers; (e) plasticizers; (t)fillers; (g) flame retardants; and (h) processing aids. The resultingpolyester polyols formed as a result of the reaction product of the oneor more carboxylic acids with one or more diols preferably haverepeating units containing eight carbon atoms or less.

The term “carboxylic acid” as used herein, and unless otherwiseindicated, preferably means a carboxylic acid, and more preferably adicarboxylic acid, having no more than six carbon atoms when reactedwith a diol, wherein the repeating units of the polyester polyol formedby the aforesaid reaction has no more than eight carbon atoms.

The term “diol” as used herein, and unless otherwise indicated, topreferably mean diols having no more than six carbon atoms when reactedwith a carboxylic acid, wherein the repeating units of the polyesterpolyol formed by the aforesaid reaction has no more than eight carbonatoms.

The term “polyester polyol” as used herein is intended to preferablymean polymeric polyester polyols having a molecular weight (determinedby the ASTM D-4274 method) falling in the range of about 300 to about4,000; more preferably from about 400 to about 2,000; and still morepreferably between about 500 to about 1,500.

The term “thermoplastic” as used herein is generally intended to meanthat the material is capable of being softened by heating and hardenedby cooling through a characteristic temperature range, and as such inthe softened state can be shaped into various articles under varioustechniques.

The term “thermoset” as used herein is generally intended to mean apolymeric material that will not flow upon the application of heat andpressure after it is substantially reacted.

The term “extender” or “difunctional extender” is used preferably in thecommonly accepted sense to one skilled in the art and includes glycols,diamines, amino alcohols and the like. Preferably, any such extender ordifunctional extender employed in accordance with the teachings of thepresent invention will have a molecular weight generally falling in therange of from about 60 to about 400.

The term “soft segment” as used herein is generally intended to mean thecomponent of the formulation exhibiting a molecular weight fromapproximately 300-4000 that contains approximately two or more activehydrogen groups per molecule prior to reaction that provides theelastomeric character of the resulting polymers.

Preferably, the membranes described herein may be useful as componentsfor footwear. In such applications, the membranes preferably are capableof containing a captive gas for a relatively long period of time. In ahighly preferred embodiment, for example, the membrane should not losemore than about 20% of the initial inflated gas pressure over a periodof approximately two years. In other words, products inflated initiallyto a steady state pressure of between 20.0 to 22.0 psi should retainpressure in the range of about 16.0 to 18.0 psi for at least about twoyears.

Additionally, the materials utilized for products such as components ofathletic shoes should be flexible, relatively soft and compliant andshould be highly resistant to fatigue and be capable of being welded toform effective seals typically achieved by RF welding or heat sealing.The material should also have the ability to withstand high cycle loadswithout failure, especially when the material utilized has a thicknessof between about 5 mils to about 200 mils.

Another preferred characteristic of the membrane is the ability to beprocessable into various shapes by techniques used in high volumeproduction. Among these techniques known in the art are extrusion, blowmolding, injection molding, vacuum molding, rotary molding, transfermolding, pressure forming, heat-sealing, casting, low pressure casting,spin casting, reaction injection molding and RF welding, among others.

As discussed above, a preferred characteristic of the membranes, whethermonolayer or multi-layer in construction, is their ability underembodiments to be formed into products which are inflated (such ascushioning devices for footwear) and which control diffusion of mobilegases through the membrane. By the present invention, not only are supergases usable as captive gases, but nitrogen gas and air, among others,may also be used as captive gases due to the performance of thematerials.

Another feature of the monolayer membranes of the present invention iselimination of many of the processing concerns presented by multi-layerembodiments. Monolayer membranes can generally be processed withoutrequiring special mechanical adapters for processing equipment and otherprocess controls. Further, products formed from monolayer embodimentsare not subject to delamination and can, at least in the case ofthermoplastics, be recycled and reground for subsequent inclusion in avariety of products.

With regard to multiple layer embodiments, a further feature of thepresent invention is the enhanced bonding which can occur betweencontiguous layers, thus, potentially eliminating the need for adhesivetie layers. This so-called enhanced bonding is generally accomplished bybringing the first and second layers together into intimate contactusing conventional techniques wherein the materials of both layers haveavailable functional groups with hydrogen atoms that can participate inhydrogen bonding such as hydrogen atoms in hydroxyl groups or hydrogenatoms attached to nitrogen atoms in urethane groups and various receptorgroups such as oxygen atoms in hydroxyl groups, carboxyl oxygens inurethane groups and ester groups, and chlorine atoms in PVDC, forexample. Such laminated membranes are characterized in that hydrogenbonding is believed to occur between the first and second layers. Forexample, the above described hydrogen bonding will theoretically occurwhere the first layer comprises a polyester polyol based urethane andthe second layer includes a barrier material such as one selected fromthe group consisting of co-polymers of ethylene and vinyl alcohol,polyvinylidene chloride, co-polymers of acrylonitrile and methylacrylate, polyethylene terephthalate, aliphatic and aromatic polyamides,crystalline polymers and polyurethane engineering thermoplastics. Inaddition to the occurrence of hydrogen bonding, it is theorized thatthere will also generally be a certain amount of covalent bondingbetween the first and second layers if, for example, there arepolyurethanes in adjacent layers or if one of the layers includespolyurethane and the adjacent layer includes a barrier material such ascopolymers of ethylene and vinyl alcohol.

This invention has many other advantages which will be more apparentfrom consideration of the various forms and embodiments of the presentinvention. Again, while the embodiments shown in the accompanyingdrawings which form a part of the present specification are illustrativeof embodiments employing the membranes of the present invention, itshould be clear that the membranes have extensive applicationpossibilities. Various exemplary embodiments will now be described ingreater detail for the purpose of illustrating the general principles ofthe invention, without considering the following detailed description inthe limiting sense.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of an athletic shoe with a portion ofthe midsole cut away to illustrate a cross-sectional view;

FIG. 2 is a bottom elevational view of the athletic shoe of FIG. 1 witha portion cut away to expose another cross-sectional view;

FIG. 3 is a section view taken alone line 3—3 of FIG. 1;

FIG. 4 is a fragmentary side perspective view of one embodiment of atubular-shaped, two-layer cushioning device;

FIG. 5 is a sectional view taken along line 4—4 of FIG. 4;

FIG. 6 is a fragmentary side perspective view of a second embodiment ofa tubular-shaped, three-layer cushioning device;

FIG. 7 is a sectional side view taken along line 6—6 of FIG. 6;

FIG. 8 is a perspective view of a membrane embodiment according to thepresent invention formed into a shoe cushioning device;

FIG. 9 is a side view of the membrane illustrated in FIG. 8;

FIG. 10 is a perspective view of a membrane embodiment according to thepresent invention formed into a shoe cushioning device;

FIG. 11 is a side elevational view of a membrane embodiment according tothe present invention formed into a cushioning device which isincorporated into a shoe;

FIG. 12 is a perspective view of the membrane illustrated in FIG. 11;

FIG. 13 is a top elevation view of the membrane illustrated in FIGS. 11and 12;

FIG. 14 is a side elevation view of a membrane embodiment according tothe present invention formed into a cushioning device incorporated intoa shoe;

FIG. 15 is a perspective view of the membrane illustrated in FIG. 14;

FIG. 16 is a top view of the membrane illustrated in FIGS. 14 and 15;

FIG. 17 is a perspective view of a membrane embodiment according to theteachings of the present invention formed into a shoe cushioning device;

FIG. 18 is a side view of the membrane illustrated in FIG. 17;

FIG. 19 is a sectional view of a product formed from a laminatedmembrane according to the teachings of the present invention;

FIG. 20 is a sectional view of a second product manufactured using alaminated membrane according to the teachings of the present invention;

FIG. 21 is a side elevation view of a sheet co-extrusion assembly;

FIG. 22 is a cross-sectional view of the manifold portion of the sheetco-extrusion assembly of FIG. 22;

FIG. 23 is a side elevation view of a tubing co-extrusion assembly;

FIG. 24 is a sectional view of a monolayer tubular membrane; and

FIG. 25 is a sectional view of a product formed from a monolayermembrane according to the teachings of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1-3, there is shown an athletic shoe, including asole structure and a cushioning device as one example of a productformed from a membrane in accordance with the teachings of the presentinvention. The shoe 10 includes a shoe upper 12 to which the sole 14 isattached. The shoe upper 12 can be formed from a variety of conventionalmaterials including, but not limited to, leathers, vinyls, nylons andother generally woven fibrous materials. Typically, the shoe upper 12includes reinforcements located around the toe 16, the lacing eyelets18, the top of the shoe 20 and along the heel area 22. As with mostathletic shoes, the sole 14 extends generally the entire length of theshoe 10 from the toe region 20 through the arch region 24 and back tothe heel portion 22.

The sole structure 14 is shown to include one or more selectivelypermeable cushioning devices or membranes 28, which are generallydisposed in the midsole of the sole structure. By way of example, themembranes 28 of the present invention can be formed into products havingvarious geometries such as the plurality of tubular members which arepositioned in a spaced apart, parallel relationship to each other withinthe heel region 22 of the midsole 26 as illustrated in FIGS. 1-3. Thetubular members are sealed to contain an injected captive gas. Thebarrier properties of the membrane 28 are preferably provided by asingle or monolayer embodiment 30A as shown in FIG. 24 or by the layer30 as shown in FIGS. 4-5 which is disposed along the inner surface of athermoplastic outer layer 32. As illustrated in FIGS. 8-18, themembranes 28 of the present invention, whether monolayer or multi-layerembodiments, can be formed into a variety of products having numerousconfigurations or shapes. As should be appreciated at this point,membranes 28 which are formed into cushioning devices employed infootwear may either be fully or partially encapsulated within themidsole or outsole of the footwear.

Referring again to FIGS. 1-3, a membrane 28 in accordance with teachingsof the present invention is illustrated as being in the form of acushioning device such as those useful as components of footwear. Themembrane 28, according to the embodiment illustrated in FIG. 24,comprises a single layer 30 A formed from one or more polyester polyolbased urethanes. The polyester polyol based urethanes are preferablyformed by the reaction product of: (a) one or more carboxylic acidshaving six or less carbon atoms with one or more diols having six orless carbon atoms; (b) at least one isocyanate and/or diisocyanate; and(c) optionally, but preferably, one or more extenders. Optionally, thepolyester polyol based urethanes may also employ one or more of thefollowing: (d) hydrolytic stabilizers; (e) plasticizers; (f ) fillers;(g) flame retardants; and (h) processing aids. As previously noted, thepolyester polyol is preferably formed as the reaction product of one ormore carboxylic acids with one or more diols, wherein the total numberof carbon atoms contained in the repeating units of polyester polyol inthe reaction product is eight or less. In addition to the one or morediols, the reaction product may also include a relatively small amountof one or more polyfunctional materials such as triols, i.e. no morethan 5.0 equivalent percent based on the total for the reaction productand active hydrogen containing groups.

Among the carboxylic acids which are considered to be useful in formingpolyester polyol based urethanes under the present invention, thoseincluding adipic, glutaric, succinic, malonic, oxalic and mixturesthereof are considered to be particularly useful.

Among the diols which are considered to be useful in forming thepolyester polyol based urethanes under the present invention, thoseincluding ethylene glycol, propanediol, butanediol, neopentyldiol,pentanediol and hexanediol and mixtures thereof are considered to beparticularly useful. Among the triols which are considered useful informing the polyester polyol based urethanes are those includingtrimethylol propane are considered to be particularly useful.

Under preferred embodiments, the polyester polyol based thermoplasticurethane employed in forming layer 30A for monolayer applications and 30for multi-layer applications will include ethylene glycol adipate. Inthis regard, certain commercially available ethylene glycol adipatessuch as FOMREZ® 22-112 and 22-225 available from Witco Chemical areconsidered to be useful.

Among the isocyanates and, more particularly, diisocyanates employed inaccordance with the teachings of the present invention, those includingisophorone diisocyanate (IPDI), methylene bis 4-cyclohexyl isocyanate(H₁₂MDI), cyclohexyl diisocyanate (CHDI), hexamethylene diisocyanate(HDI), m-tetramethyl xylene diisocyanate (m-TMXDI), p-tetramethyl xylenediisocyanate (P-TMXDI), and xylylene diisocyanate (XDI) are consideredto be useful; particularly useful is diphenylmethane diisocyanate (MDI).Preferably, the isocyanate(s) employed are proportioned such that theoverall ratio of equivalents of isocyanate to equivalents of activehydrogen containing materials is within the range of 0.95:1 to 1.10:1,and more preferably, 0.98:1 to 1.04:1. As is known in the urethanechemistry art, the phrase “active hydrogen containing groups” generallyrefers to groups including amines and alcohols collectively, which arecapable of reacting with the isocyanate groups.

Optionally, but often preferably, hydrolytic stabilizers will beincluded in the polyester polyol based polyurethanes of the presentinvention. For example, two commercially available carbodiimide basedhydrolytic stabilizers known as STABAXOL P and STABAXOL P-100, which areavailable from Rhein Chemie of Trenton, N. J., have proven to beeffective at reducing the susceptibility of the material to hydrolysis.Still other hydrolytic stabilizers such as those which are carbodiimideor polycarbodiimide based, or based on epoxidized soy bean oil areconsidered useful. The total amount of hydrolytic stabilizer employedwill generally be less than 5.0 wt. % of the composition's total.

In addition to hydrolytic stabilizers, generally various plasticizerscan be included for purposes of increasing the flexibility anddurability of the final product as well as facilitating the processingof the material from a resinous form to a membrane or sheet. By way ofexample, and without intending to be limiting, plasticizers such asthose based on butyl benzoyl phthalate have proven to be particularlyuseful. Regardless of the plasticizer or mixture of plasticizersemployed, the total amount of plasticizer, if any, will generally beless than 40.0 wt. % of the composition's total.

Fillers may also be employed in the polyester polyol based polyurethanesof the present invention, especially with regard to monolayerapplications wherein hydrogen bonding between layers is not a concern.Included in the class of materials generally referred to herein as“fillers” are fibrous and particulate materials, non-polar polymericmaterials and inorganic anti-block agents. Examples of such materialsinclude glass and carbon fibers, glass flakes, silicas, calciumcarbonate, clay, mica, talc, carbon black, particulate graphite andmetallic flakes, among others. In the event that fillers are employed,generally the total amount of fillers will be less than 60.0 wt % of thetotal composition weight.

Yet another class of components which may be employed in the polyesterpolyol based urethane compositions of the present invention includeflame retardants as the term is understood in the art. While the amountof any flame retardants employed is generally dependent upon the desireduse of the final product, the total amount of flame retardantcontemplated for any application would be 40.0 wt. % or less based onthe total weight of the composition. Among the numerous flame retardantswhich are considered useful, those based on phosphorous or halogenatedcompounds and antimony oxide based compositions are considered to beparticularly useful.

With regard to the use of additives, otherwise referred to herein asprocessing aids, minor amounts of antioxidants, UV stabilizers, thermalstabilizers, light stabilizers, organic anti-block compounds, colorants,fungicides, mold release agents and lubricants as are known in the artmay be employed wherein the total constituency of all such processingaids is generally less than 3.0 wt. %.

It may also be desirable to include a catalyst in the reaction mixtureto prepare the compositions of the present invention. Any of thecatalysts conventionally employed in the art to catalyze the reaction ofan isocyanate with a reactive hydrogen containing compound can beemployed for this purpose; see, for example, Saunders et al.,Polyurethanes, Chemistry and Technology, Part I, Interscience, New York,1963, pages 228-232; see also, Britain et al., J. Applied PolymerScience, 4, 207-211, 1960. Such catalysts include organic and inorganicacid salts of, and organometallic derivatives of, bismuth, lead, tin,iron, antimony, uranium, cadmium, cobalt, thorium, aluminum, mercury,zinc, nickel, cerium, molybdenum, vanadium, copper, manganese andzirconium, as well as phosphines and tertiary organic amines.Representative organotin catalysts are stannous octoate, stannousoleate, dibutyltin dioctoate, dibutyltin dilaurate, and the like.Representative tertiary organic amine catalysts are triethylamine,triethylenediamine, N₁N₁N′₁N′-tetramethylethylenediamine,N₁N₁N′₁N′-tetraethylethylenediamine, N-methyl-morpholine,N-ethylmorpholine, N₁N₁N′₁N′-tetramethylguanidine, andN₁N₁N′₁N′-tetramethyl-1,3-butanediamine.

Regardless of the catalyst(s) which is utilized, if any, the weightpercentage of such material is typically less than one half of onepercent by weight (0.5 wt. %) based on the total weight of the polyesterpolyol based thermoplastic urethane reaction mixture.

Among the extenders which are optionally, but preferably, employed inaccordance with the teachings of the present inventions are thosegenerally selected from the group consisting of alcohols and amines. Forexample, alcohol based extenders may include ethylene glycol,1,3-propylene glycol, 1,2-propylene glycol, 1,4-butanediol,1,6-hexanediol, neopentyl glycol, and the like; and dihydroxyalkylatedaromatic compounds such as the bis (2-hydroxyethyl) ethers ofhydroquinone and resorcinol; p-xylene-α,α′-diol; the bis(2-hydroxyethyl) ether of p-xylene-α, α′-diol; m-xylene-α,α′-diol andthe bis (2-hydroxyethyl) ether and mixtures thereof. Illustrative ofdiamine extenders are aromatic diamines such as p-phenylenediamine,m-phenylenediamine, benzidine, 4,4′-methylenedianiline,4,4′-methylenibis (2-chloroaniline) and the like. Illustrative ofaliphatic diamine extenders is ethylene diamine. Illustrative of aminoalcohols are ethanolamine, propanolamine, butanolamine, and the like.

Preferred extenders include ethylene glycol, 1,3-propylene glycol,1,4-butanediol, 1,6-hexanediol, and the like.

In addition to the above-described extenders, a small amount oftrifunctional extenders such as trimethylol propane, 1,2,6 hexanetrioland glycerol, may also be present. The amount of trifunctional extendersemployed would preferably be 5.0 equivalent percent or less based on thetotal weight of the reaction product and active hydrogen containinggroups employed.

Generally, the ratio of polyester polyol to extender can be variedwithin a relatively wide range depending largely on the desired hardnessof the final polyurethane elastomer. As such, the equivalent proportionof polyester polyol to extender should be within the range of 1:0 to1:12 and, more preferably, from 1:1 to 1:8.

In addition to the at least one polyester polyol based urethane, thelayer 30A of FIG. 24 may contain one of the following and layer 30 ofFIGS. 4 and 5 will also preferably contain one or more materialsselected from the group consisting of co-polymers of ethylene and vinylalcohol, polyvinylidene chloride, co-polymers of acrylonitrile andmethyl acrylate, polyethylene terephthalate, aliphatic and aromaticpolyamides, crystalline polymers and polyurethane engineeringthermoplastics. Such materials are preferably blended with the polyesterpolyol based urethane constituent utilizing conventional blendingtechniques prior to forming the membranes.

For monolayer embodiments 30A, it is preferred that the total amount ofone or more of the above listed materials be up to about 30.0 wt. %,since higher amounts tend to result in products which are somewhatinflexible. In multi-layer embodiments, however, the total amount of oneor more of the above listed materials in a blended layer may be up toabout 95.0 wt. %. Thus, for multi-layer constructions, layer 30 whichpreferably employs blends of at least one polyester polyol basedurethane and one or more of the above-listed materials will generallyinclude up to 70.0 wt. % polyester polyol based thermoplastic urethanebut, more preferably, will include between about 1.0 wt. % to about 50.0wt. % polyester polyol based thermoplastic urethanes. Under highlypreferred embodiments, the polyester polyol based thermoplastic urethaneconstituency of the layer 30 will be present in the range of betweenabout 5.0 wt. % to about 25.0 wt. %.

Of the various materials which are considered to be useful in blendedassociation with the polyester polyol based urethanes, copolymers ofethylene and vinyl alcohol and materials including mixtures ofethylene-vinyl alcohol copolymers are generally preferred.

Commercially available products based on copolymers of ethylene andvinyl alcohol such as SOARNOL™ which is available from the Nippon GohseiCo., Ltd. (U.S.A.) of New York, N.Y., and EVAL® which is available fromEval Company of America, Lisle, Ill. have proven to be useful. Highlypreferred commercially available copolymers of ethylene and vinylalcohol such as EVAL® LCF101A will typically have an average ethylenecontent of between about 25 mol % to about 48 mol %.

Other materials useful for blending with one or more polyester polyolbased urethanes as described above which are commercially availableinclude BAREX™ 210 which is a copolymer of acrylonitrile and methylacrylate available from the British Petroleum Co. and ISOPLAST™ which isa polyurethane engineering thermoplastic available from the Dow ChemicalCo.

In addition to blending the materials selected from the group consistingof co-polymers of ethylene and vinyl alcohol, polyvinylidene chloride,co-polymers of acrylonitrile and methyl acrylate, polyethyleneterephthalate, aliphatic and aromatic polyamides, crystalline polymersand polyurethane engineering thermoplastics with polyester polyol basedurethanes as described above, it should be recognized by those skilledin the art that such materials can be utilized for the production ofseparate layers for lamination in multi-layer embodiments as describedherein.

While it is generally preferred that the polyurethanes employed for boththe monolayer and multi-layer embodiments are based on aromaticisocyanates such as diphenylmethane diisocyanate (MDI), in certainmulti-layer constructions, it may be desirable to use aliphaticpolyurethanes in combination with the above described barrier materials.More particularly, polyurethanes based on aliphatic isocyanates wouldpreferably be employed where it is contemplated that aromaticisocyanates beyond a certain concentration would react with the barriermaterial employed. For example, and without intending to be limiting,when a blended layer includes a concentration of 5.0 wt. % of copolymersof ethylene and vinyl alcohol, polyurethanes based on aliphaticisocyanates would be preferred. It may, however, be beneficial toinclude a relatively small amount of at least one aromatic thermoplasticpolyurethane (i.e. those derived from aromatic isocyanates) as aviscosity modifier. Thus, the preferred composition of a blended layerincluding at least 5 wt. % of at least one copolymer of a reactivebarrier material such as a co-polymer of ethylene and vinyl alcohol canbe summarized as including: (a) at least 50 wt. % of at least onebarrier material selected from the group consisting of co-polymers ofethylene and vinyl alcohol, polyvinylidene chloride, co-polymers ofacrylonitrile and methyl acrylate, polyethylene terephthalate, aliphaticand aromatic polyamides, crystalline polymers and polyurethaneengineering thermoplastics; (b) 1 wt. % to about 50 wt. % of at leastone aliphatic thermoplastic urethane; and (c) up to about 3 wt. % ofaromatic thermoplastic urethanes, wherein the total constituency of theblended layer is equal to 100 wt. %. The aromatic thermoplasticurethanes are also typically selected from the group consisting ofpolyester, polyether, polycaprolactone, polyoxypropylene andpolycarbonate macroglycol based materials and mixtures thereof.

Additionally, it may be desirable under certain applications to includeblends of polyurethanes to form layers 30A and 30, respectively, such aswhere susceptibility to hydrolysis is of particular concern. Forexample, a polyurethane including soft segments of polyether polyols orpolyester polyols formed from the reaction mixture of a carboxylic acidand a diol wherein the repeating units of the reaction product has morethan eight carbon atoms can be blended with polyurethanes includingpolyester polyols having eight or less carbon atoms. Preferably, thepolyurethanes other than those including polyester polyol repeatingunits having eight or less carbon atoms will be present in the blends inan amount up to about 30 wt. %, (i.e. 70.0 wt. % polyethylene glycoladipate based urethane 30.0% isophthalate polyester polyol basedurethane). Specific examples of the polyester polyols wherein thereaction product has more than eight carbon atoms include poly(ethyleneglycol isophthalate), poly(1,4 butanediol isophthalate) and poly(1,6hexanediol isophthalate).

Additionally, rather than using blends of various thermoplasticurethanes, it is also possible to utilize a single polyurethane whereinvarious soft segments are included therein. Again, without intending tobe limiting, the soft segments may include, in addition to soft segmentshaving a total of eight carbon atoms or less, polyether polyols,polyester polyols having a total of more than eight carbon atoms, ormixtures thereof. It is contemplated that the total amount of softsegment constituency which includes the reaction product of a carboxylicacid and a diol having a total carbon atom count of more than eight, bepresent in an amount of up to about 30 wt. % of the total weight of softsegments included in the polyurethane. Thus, at least 70 wt. % of thesoft segment repeating units will be the reaction products of carboxylicacid and a diol, wherein the total carbon atom count for the reactionproduct is eight or less.

It should also be noted that there are a number of ways to addpolyurethanes with up to 30 wt. % of polyesters with repeat unitscontaining more than eight carbon atoms to the polyurethanes of thisinvention. Thirty percent or less of a polyurethane derived frompolyester polyols containing repeat units with more than eight carbonscan be blended as finished polymers with 70 wt. % or more ofpolyurethanes derived from polyester polyols with repeat unitscontaining eight or less carbon atoms, or a single polyurethane could beprepared from a mixture of polyester polyols wherein 70 wt. % or morecontain repeat units with eight carbons or less and the balance containsrepeat units with more than eight carbons as described previously. Apolyurethane could be prepared from a single polyol prepared by reactionfrom dicarboxylic acids and diols such that 70 wt. % of the repeat unitsin the polyester polyol contain eight or less carbon atoms. Combinationsof these techniques are also possible. Among the acids that contain morethan six carbon atoms that could be employed are isophthalic a andphthalic acids.

As discussed, the membranes 28 of the present invention may also be inthe form of multi-layer constructions. For example, membranes 28 and Aof FIGS. 4-7 include a layer 32 formed of a flexible resilientelastomeric material which preferably is resistant to expansion beyond apredetermined maximum volume when the membrane is subjected to gaseouspressure.

The layer 32 preferably is formed of a material or combination ofmaterials which offer superior heat sealing properties, flexural fatiguestrength, a suitable modulus of elasticity, tensile and tear strengthand abrasion resistance. Among the available materials which offer thesecharacteristics, it has been found that thermoplastic elastomers of theurethane variety, otherwise referred to herein as thermoplasticurethanes or simply TPU's, are highly preferred because of theirexcellent processability.

Among the numerous thermoplastic urethanes which are useful in formingthe outer layer 32, urethanes such as PELLETHANE™ 2355-ATP, 2355-95AEand 2355-854A (trademarked products of the Dow Chemical Company ofMidland, Mich.), ELASTOLLAN® (a registered trademark of the BASFCorporation) and ESTANE® (a registered trademark of the B.F. GoodrichCo.), all of which are either ester or ether based, have proven to beparticularly useful. Still other thermoplastic urethanes based onpolyesters, polyethers, polycaprolactone and polycarbonate macroglycolscan be employed. Further, in addition to the commercially availablepolyurethanes, it should also be noted that layer 32 of FIG. 4 andlayers 32 and 34 of membrane A shown in FIG. 7 could also be made fromthe polyester polyol based polyurethanes containing soft segmentswherein the reaction product has eight or less carbon atoms. This wouldgenerally result in a reduction in GTR's since much of the resistance togas diffusion in multi-layer constructions comes from the barrier layer.

As previously noted, the membranes as disclosed herein can be formed byvarious processing techniques including but not limited to extrusion,blow molding, injection molding, vacuum molding and heat sealing or RFwelding of tubing and sheet extruded film materials. With regard to themulti-layer membranes described herein, such membranes are made fromfilms formed by co-extruding the material forming layer 30 together withthe material comprising layer 32. After forming the multi-layered filmmaterials, the film materials are heat sealed or welded by RF welding toform the inflatable membranes which are highly flexible in nature.

The membranes, whether in the form of sheet, substantially closedcontainers, cushioning devices, accumulators or other structures,preferably will have a tensile strength on the order of at least about2500 psi; a 100% tensile modulus of between about 350-3000 psi and/or anelongation of at least about 250% to about 700%.

Referring now to FIGS. 6 and 7, an alternative membrane embodiment A inthe form of an elongated tubular shaped multi-layered component isillustrated. The modified membrane A is essentially the same as themembrane 28 illustrated in FIGS. 4 and 5 except that a third layer 34 isprovided contiguously along the inner surface of the layer 30, such thatlayer 30 is sandwiched between an outer layer 32 and an innermost layer34. The innermost layer 34 is also preferably made from a thermoplasticurethane material. In addition to the perceived benefit of enhancedprotection against degradation of layer 30, layer 34 also tends toassist in providing for high quality welds which facilitate theformation of three-dimensional shapes for products such as cushioningdevices useful in footwear.

Membranes such as those shown in FIGS. 1-7 and FIG. 24 are preferablyfabricated from extruded tubes. Lengths of the tubing which typicallyrange from about one foot up to about five feet in length. Membranes canthen be inflated to a desired initial inflation pressure ranging from 0psi ambient to 100 psi, preferably in the range of 5 to 50 psi, with thecaptive gas preferably being nitrogen. Sections of the tubing arethereafter RF welded or heat sealed to the desired lengths. Theindividual membranes produced upon RF welding or heat sealing are thenseparated by cutting through the welded areas between adjacentmembranes. It should also be noted that the membranes can be fabricatedfrom so-called flat extruded tubing as is known in the art whereby theinternal geometry is welded into the tube.

With regard to extruding the multi-layer embodiments described herein,as the material which forms layers 30, 32 and optionally, layer 34advance to the exit end of the extruder through individual flowchannels, once they near the die-lip exit, the melt streams are combinedand arranged to float together in layers typically moving in a laminarflow as they enter the die body. Preferably, the materials are combinedat a temperature of between about 300° F. to about 465° F. and apressure of at least about 200 psi to obtain optimal wetting for maximumadhesion between the contiguous portions of the layers 30, 32 and 34respectively and further to enhance hydrogen bonding between the layerswherein the materials employed are conducive to hydrogen bonding. Again,for multi-layered laminates, it is preferred that the polyester polyolsutilized in the polyurethanes of layers 30, 32 and 34 be highlyaliphatic in nature, since aliphatic urethanes have been found to bereadily processable utilizing conventional techniques such as sheetextrusion.

To this end, it is believed that hydrogen bonding occurs between therespective layers as the result of available functional groups withhydrogen atoms that can participate in hydrogen bonding such as hydrogenatoms in hydroxyl groups or hydrogen atoms attached to nitrogen atoms inurethane groups and various receptor groups such as oxygen atoms inhydroxyl groups, carbonyl oxygens in urethane groups and ester groupsand chlorine atoms in PVDC, for example.

The chemical reaction provided below illustrates the theoretical surfacebond which is believed to occur between layers 32 and 34 with layer 30across substantially the entire intended contact surface area of themembrane:

and R′ is a short chain diol such as (CH₂)₄

In addition to the hydrogen bonding as illustrated above, to a morelimited extent, it is believed that a certain amount of covalent bondsare formed between the second and third layers 32 and 34, respectively,with the first layer 30. Still other factors such as orientation forcesand induction forces, otherwise known as van der Waals forces, whichresult from London forces existing between any two molecules anddipole-dipole forces which are present between polar molecules arebelieved to contribute to the bond strength between contiguous layers ofthermoplastic urethane and the main layer.

The hydrogen bonding as described above is in contrast to prior artembodiments which, failing to recognize the existence and/or potentialof such bonding, typically have required the use of adhesive tie-layerssuch as Bynel®, for example, to maintain the bonding between the variouslayers.

As noted above, since fillers tend to negatively effect the so-calledhydrogen bonding capacity of multi-layer embodiments, while the use ofup to about 60.0 wt. % of fillers in monolayer embodiments iscontemplated, the use of fillers in processing multi-layer membraneswhere hydrogen bonding is desired should be limited, if used at all.

Referring to FIGS. 12-16, membranes in the form of air bladders arefabricated by blow molding are shown. To form the bladders, single layerparisons are extruded or parisons of two layer or three layer film areco-extruded as illustrated in FIGS. 21-23. Thereafter, the parisons areblown and formed using conventional blow molding techniques. Theresulting bladders, examples of which are shown in FIGS. 12 and 15, arethen inflated with the desired captive gas to the preferred initialinflation pressure and then the inflation port (e.g. inflation port 38 )is sealed by RF welding.

Still other embodiments formed from the membranes described herein areshown in FIGS. 8-10. Sheets or films of extruded monolayer film orco-extruded two layer or three layer film are formed to the desiredthicknesses. For example, the thickness range of the co-extruded sheetsor films is preferably between 0.5 mils to 10 mils for the layer 30 andbetween 4.5 mils to about 100 mils for the layers 32 and 34,respectively. For monolayer cushioning device embodiments, the averagethickness will generally be between 5 mils to about 60 mils and, morepreferably, between about 15 mils and to about 40 mils.

Still another embodiment formed from a membrane of the present inventionis shown in FIGS. 17 and 18. The air bladder is fabricated by formingextruded single layer or co-extruded multiple layer tubing having adesired thickness range. The tubing is collapsed to a lay flatconfiguration and the opposite walls are welded together at selectedpoints and at each end using conventional heat sealing or RF weldingtechniques. The cushioning device is then inflated through a formedinflation port 38 to the desired inflation pressure which ranges from 0psi ambient to 100 psi, and preferably from 5 to 50 psi, with a captivegas such as nitrogen.

In addition to employing the membranes of the present invention ascushioning devices or air bladders as described above, still anotherhighly desirable application for the membranes of the present inventionis for accumulators as illustrated in FIGS. 19, 20 and 25.

Referring to FIG. 25, there is shown an accumulator embodiment formedfrom a monolayer membrane as described above. Likewise, referring toFIGS. 19 and 20, there are shown two alternative accumulator embodimentsformed from a multi-layer membrane of the present invention.Accumulators, and more particularly, hydraulic accumulators are used forvehicle suspension systems, vehicle brake systems, industrial hydraulicaccumulators or for other applications having differential pressuresbetween two potentially dissimilar fluid media. The membrane 124separates the hydraulic accumulator into two chambers or compartments,one of which contains a gas such as nitrogen and the other one of whichcontains a liquid. Membrane 124 includes an annular collar 126 and aflexible body portion 128. Annular collar 126 is adapted to be securedcircumferentially to the interior surface of the spherical accumulatorsuch that body portion 128 divides the accumulator into two separatechambers. The flexible body portion 128 moves generally diametricallywithin the spherical accumulator and its position at any given time isdependant upon the pressure of the gas on one side in conjunction withthe pressure of the liquid on the opposite side.

By way of further example, FIG. 20 illustrates a product in the form ofa hydraulic accumulator including a first layer 114 made from thematerials described with reference to layers 30A and 30 as describedabove. Additionally, the product includes layers 112 and 116 formed fromone or more thermoplastic urethanes, one or more barrier materials or acombination of at least one urethane and barrier material as describedwith reference to layers 32 and 34 above. As shown, the first layer 114only extends along a segment of the entire accumulator body portion. Itmay be desirable to utilize such embodiments, otherwise referred toherein as “intermittent constructions” under circumstances where thedelamination potential along certain segments of a product is greatest.One such location is along the annular collar 126 of the bladder ordiaphragm for hydraulic accumulators in multi-layer embodiments. Thus,while the multi-layer membranes of the present invention are generallymore resistant to delamination and do a better job of preventing gasfrom escaping along interfaces between layers such as those occurringalong the annular collar via capillary action, it should be recognizedthat the membranes 110 described herein can include segments which donot include layer 114.

To form the membranes 110 which are subsequently formed into theproducts illustrated in FIGS. 19, 20 and 25, a number of differentprocesses can be used, including but not limited to, extrusion andco-extrusion blow molding utilizing continuous extrusion, intermittentextrusion utilizing (1) reciprocating screw systems; (2) ramaccumulator-type systems; and (3) accumulator head systems, co-injectionstretch blow molding, extruded or co-extruded sheet, blown film, tubingor profiles. With regard to multi-layer processes, it has been foundthat utilizing co-extrusions give rise to products which appear todemonstrate the above desired hydrogen bonding between the respectivelayers 114 and, 112 and 116, respectively, when conducive materials areutilized. To form a product such as a hydraulic accumulator bladder ordiaphragm via a multi-layer process, such as blow molding, any one of anumber of commercially available blow molding machines such as a BekumBM502 utilizing a co-extrusion head model No. BKB95-3B1 (not shown) or aKrup KEB-5 model utilizing a model No. VW60/35 co-extrusion head (notshown) could be utilized.

As previously noted, the manufacture of monolayer membranes generallyresembles the manufacture of multi-layer membranes but requires farfewer process controls. For example, monolayer membranes require only asingle extruder with no feed block being required. Sheet can be made byforcing molten polymer formed in the extruder through a coat hanger die.Collapsed tubing and parisons used in blow molding are made by forcingmolten plastic generated by an extruder through an annular die.

A brief description of preferred multi-layer processing techniques willnow be provided. Initially, the resinous materials to be extruded arefirst dried to the manufacturer's specification (if necessary) and fedinto the extruder. Typically, the materials are fed into the extrudersaccording to the order in which the layers are to be arranged. Forexample, with regard to a three layer embodiment, a material includingpolyester polyol based urethane is fed to an outside extruder, amaterial such as a TPU and/or one or more barrier materials is fed to amiddle extruder and a material such as a TPU is fed to an insideextruder. The extruder heat profile is set for the best processing ofthe individual materials. It is suggested, however, that no more than a20° F. difference be present at the exit point of each extruder. As thematerial is forced forward in each extruder, the heat profile is set toachieve the best molten mass. The heat profile would typically be setfor between 300° F. to about 465° F. with the feed zone being the lowestset point and all other set points gradually increasing in increments ofapproximately 10° F. until the desired melt is achieved. Once leavingthe extruders a section of pipes is sometimes used to direct thematerial to the multi-layered head (i.e. three or more heads). It is atthis point that any adjustments for differences in heat are addressed.The pumping action of the extruders not only forces the material intothe individual head channels or flow paths but also determines thethickness of each layer. As an example, if the first extruder has a 60mm diameter, the second extruder has a 35 mm diameter and the thirdextruder has a 35 mm diameter, the speeds required to produce a 1.3liter bladder or diaphragm requiring 2 mm for the outside layer, 3 milsfor the middle layer and 2 mm for the inside layer for the variousextruder would be approximately 26 seconds for the first extruder havinga screw speed of about 10 rpm's, the second extruder would have a screwspeed of about 5 rpm's and the third extruder would have a screw speedof about 30 rpm. Once the materials enter the head channels or flowpaths, the heat would normally be held constant or be decreased toadjust for the melt strength of the materials. The individual headchannels or flow paths keep separate the molten masses while directingthem downward and into the shape of a parison.

Just prior to entering the lower die or bushing and the lower mandrel,the material head channels or flow paths are brought together under thepressure created by the now unitary flow path surface area, the gapbetween the lower bushing and mandril and the pressure on the individuallayers from the respective extruders. This pressure must be at least 200psi and is normally, under the conditions described, in excess of 800psi. At the point where the materials come together, one parison is nowformed that is a laminate made up of the three layers. The upper limitof the pressure is essentially only constrained by the physical strengthof the head. After exiting the head, the laminate is closed on each endby the two mold halves and a gas such as air is injected into the moldforcing the laminated parison to blow up against the mold and be held inthis fashion until sufficient cooling has taken place (i.e.approximately 16 seconds for the aforementioned sample), at which pointthe gas is exhausted. The part is then removed from the mold and furthercooling is allowed for sufficient time to allow for the part to bede-flashed or further processed as some parts may require. As should nowbe understood by those skilled in the art, the layers must be heldseparate until fully melted and preformed into a hollow tube at whichtime they are bonded together under the heat and pressure describedherein.

As those skilled in the plastic forming industry will recognize, thethree major components of a blow molding machine, namely the extruders,die heads and mold clamps, come in a number of different sizes andarrangements to accommodate for the consumer production rate scheduleand size requirements.

A multi-layer process known as sheet co-extrusion is also a usefultechnique to form membranes in accordance with the teachings of thepresent invention. Sheet co-extrusion generally involves thesimultaneous extrusion of two or more polymeric materials through asingle die where the materials are joined together such that they formdistinct, well bonded layers forming a single extruded product.

The equipment required to produce co-extruded sheet consists of oneextruder for each type of resin which are connected to a co-extrusionfeed block such as that shown in FIGS. 21 and 23, which are commerciallyavailable from a number of different sources including the CloreonCompany of Orange, Tex. and Production Components, Inc. of Eau Claire,Wis., among others.

The co-extrusion feed block 150 consists of three sections. The firstsection 152 is the feed port section which connects to the individualextruders and ports the individual round streams of resin to theprogramming section 154. The programming section 154 then reforms eachstream of resin into a rectangular shape the size of which is inproportion to the individual desired layer thickness. The transitionsection 156 combines the separate individual rectangular layers into onesquare port. The melt temperature of each of the TPU layers shouldgenerally be between about 300° F. to about 465° F. To optimize adhesionbetween the respective layers, the actual temperature of each meltstream should be set such that the viscosities of each melt streamclosely match. The combined laminar melt streams are then formed into asingle rectangular extruded melt in the sheet die 158 which preferablyhas a “coat hanger ” design as shown in FIG. 22 which is now commonlyused in the plastics forming industry. Thereafter the extrudate can becooled utilizing rollers 160 forming a rigid sheet by either the castingor calendaring process.

Similar to sheet extrusion, the equipment required to produceco-extruded tubing consists of one extruder for each type of resin witheach extruder being connected to a common multi-manifolded tubing die.The melt from each extruder enters a die manifold such as the oneillustrated in FIG. 23 which is commercially available from a number ofdifferent sources including Canterberry Engineering, Inc. of Atlanta,Ga. and Genca Corporation of Clearwater, Fla. among others, and flows inseparate circular flow channels 172A and 172B for the different melts.The flow channels are then shaped into a circular annulus the size ofwhich is proportional to the desired thickness for each layer. Theindividual melts are then combined to form one common melt stream justprior to the die entrance 174. The melt then flows through a channel 176formed by the annulus between the outer surface 178 of a cylindricalmandrel 180 and the inner surface 182 of a cylindrical die shell 184.The tubular shaped extrudate exits the die shell and then can be cooledinto the shape of a tube by many conventional pipe or tubing calibrationmethods. While a two component tube has been shown in FIG. 23 it shouldbe understood by those skilled in the art that additional layers can beadded through separate flow channels.

Regardless of the plastic forming process used, it is desirable that aconsistent melt of the materials employed be obtained to accomplishbonding between layers across the intended length or segment of thelaminated product. Again then, the multi-layer processes utilized shouldbe carried out at maintained temperatures of from about 300° F. to about465° F. Furthermore, it is important to maintain sufficient pressure ofat least 200 psi at the point where the layers are joined wherein theabove described hydrogen bonding is to be effectuated.

As previously noted, in addition to the excellent bonding which can beachieved for the laminated membrane embodiments of the presentinvention, another objective, especially with regard to membranesemployed as cushioning devices for footwear, is to provide membraneswhich are capable of retaining captive gases for extended periods oftime. In general, membranes which offer gas transmission rate values of15.0 or less for nitrogen gas as measured according to the proceduresdesignated at ASTM D-1434-82 for membranes having an average thicknessof 20 mils are acceptable candidates for extended life applications.Thus, while the membranes of the present invention can have varyingthicknesses depending mainly on the intended use of the final product,the membranes of the present invention will preferably have a gastransmission rate value of 15.0 or less when normalized to a thicknessof 20 mils regardless of the actual thickness of the membrane. Likewise,while nitrogen gas is the preferred captive gas for many embodiments andserves as a benchmark for analyzing gas transmission rates in accordancewith ASTM D-1434-82, the membranes can contain a variety of differentgases and/or liquids.

In this regard, because of the excellent characteristics offered by thepolyester polyol based urethanes in terms of flexibility, resistance todegradation caused by moisture and resistance to undesired gastransmissions, among others, the membranes of the present invention canbe employed as either monolayer or multi-layer embodiments. Underpreferred embodiments, the membranes of the present invention will havea gas transmission rate of 10.0 and still, more preferably, will havegas transmission rates of 7.5 or less for nitrogen gas at 20 mils. Stillmore preferably, the membranes of the present invention will have a gastransmission rate of 5.0 or less and, still more preferably yet, willhave a gas transmission rate of 2.5 or less for nitrogen gas at 20 mils.Under the most highly preferred embodiments, the membranes of thepresent invention will have a gas transmission rate of 2.0 or less fornitrogen gas for membranes having an average thickness of 20 mils.

To prepare Samples 1-12 as set forth in Table I for gas transmissionrate analysis, the polyester polyol based urethane was initiallyprepared by adding one or more of the following constituents to a 2000ml reaction flask: (1) polyester polyol (i.e. commercial product orreaction product of dicarboxylic acid and diol, as described); (2)difunctional extender; and (3) processing aids such as waxes andantioxidants. Thereafter, the hydroxyl component was heated to betweenapproximately 95° C.-115° C. (depending on the composition) and stirredto dissolve and homogenize the constituents. Subsequently, a vacuum ofless than 0.2 mm Hg was applied under constant stirring to controlfoaming. After foaming was completed, the flask was degassed forapproximately 30 minutes until virtually all bubbling ceased.

Next, the isocyanate component was prepared by disposing a diisocyanatein a 250 ml polypropylene beaker and placing the diisocyanate in an ovenheated to between approximately 50-65° C. Upon obtaining a temperatureof between about 50-65° C., the desired amount of the isocyanateconstituent was weighted out and the catalyst, if any, was added to theisocyanate constituent under constant mixing.

Once the catalyst was fully mixed in, the desired amount of hydroxylcomponent was added to the isocyanate component to effectuatepolymerization. As polymerization began and the viscosity increased(generally between about 7-12 seconds after addition), the reactionproduct was poured into pans coated with a desirable release agent andallowed to fully cool. Upon cooling, the newly formed polymer was cutinto granules and dried for approximately 2-4 hours at between 85-100°C. Thereafter, Samples 1-10, as set forth in Table I, were prepared bycompression molding granules of plastic into sheets to conduct analysisrelating to gas transmission properties.

With regard to Sample 11 as illustrated in Table I, after forming thepolyester polyol based urethane as described above, 70.0 wt. % of thematerial was blended and extruded along with the 30.0 wt. % BAREX™ 210available from BP Chemical, Inc., at a temperature of approximately 420°F. to provide a blended sample for gas transmission analysis. Further,with regard to Sample 12, a membrane was formed for gas transmissionanalysis by blending 70.0 wt. % of the polyester polyol based urethaneset forth in Sample 12 with 30.0 wt. % of the BAREX™ 210 at atemperature of approximately 420° F.

TABLE I* Gas Transmission Rates For Single Layers Formulation 1 2 3 4 56 7 8 9 10 11 12 13 14 Polybutanediol Adipate (a) 2000 m.w.¹ 43.12 (b)700 m.w.² 15.09 Ethylene Glycol Adipate (a) 1000 m.w.³ 61.11 62.29 49.1860.63 49.60 30.26 16.39 42.84 51.23 (b) 500 m.w.⁴ 22.69 32.77 HDAdipate/HD 18.36 Isophthalate (a) 1000 m.w.⁵ Ethylene 51.23 GlycolGlutarate (a) 1000 m.w.⁸ Ethylene Glycol 4.25 Dipropylene glycol 0.58Butyl Carbitol 0.21 0.25 0.25 1,4 Butanediol 7.31 6.05 9.96 6.00 8.936.81 7.37 9.22 6.06 9.22 H12MDI⁷ 41.07 39.84 MDI⁸ 33.04 32.5 40.52 43.1538.96 32.40 38.96 MDI/liq. MDI⁹ 33.12 33.03 Irganaox 1010¹⁰ 0.125 0.150.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 Advawax 280¹¹ 0.125 0.150.15 0.15 0.15 0.15 0.15 0.15 0.15 Wax¹² 0.30 0.15 Catalyst¹³ 0.04 0.040.04 0.04 0.04 0.10 0.10 0.02 0.04 0.04 0.04 Kemamide W-40¹⁴ 0.15Pellethane 2355-85 100.0 100.0 ATP¹⁵ Pellethane 2355-95 100.0 AE¹⁶ TotalWt. % 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0100.0 100.0 100.0 *All values provided in Table I are in weight percents(wt. %) ¹FOMREZ ™ 44-56 available from Witco Chemical ²FOMREZ ™ 44-160available from Witco Chemical ³FOMREZ ™ 22-112 available from WitcoChemical ⁴FOMREZ ™ 22-225 available from Witco Chemical ⁵FOMREZ ™8066-120 - 50 parts 1,6 hexanediol adipate and 50 parts HD Isophthalatepolyester polyol available from Witco Chemical ⁶UrethHall ™ 2050available from C.P. Hall Company ⁷DESMODUR W available from BAYER AG(America) ⁸ISONATE ™ 2125M available from Dow Chemical Co. ⁹Blend of 80parts ISONATE ™ 2125 and 20 parts ISONATE ™ 2143 available from DowChemical Co. ¹⁰IRGANOX ™ 1010 available from Ciba-Gigy Chemical Co.¹¹ADVAWAX ™ 280 available from Morton Plastics, Inc. ¹²Montan ester wax¹³Blend of 50 parts stannous octoate and 50 parts dioctyl phthalate¹⁴Kemamide W-40 (ethylene bis-stearamide wax) available from WitcoChemical ¹⁵PELLETHANE ™ 2355-85 ATP available from Dow Chemical Co.¹⁶PELLETHANE ™ 2355-95 AE available from Dow Chemical Co.

TABLE II GTR (cc/m² * atm * day) Sample Average Normalized to 20 milsNumber Thickness GTR (cc/m² * atm * day) thickness 1 16.25 mils 30.9525.15 2  15.2 mils 11.71 8.9 3 17.13 mils 9.13 7.82 4 18.49 mils 6.586.08 5 17.54 mils 7.07 6.19 6 19.93 mils 9.22 9.19 7 19.93 mils 6.196.17 8 18.31 mils 1.20 1.10 9 16.93 mils 3.47 2.93 10 14.47 mils 17.9212.96 11 19.22 mils 1.24 1.19 12  17.1 mils 2.73 2.33 13 19.95 mils36.42 36.33 14 18.25 mils 24.12 22.01

As illustrated in Table II, each of the Samples 2-12 demonstrated bettergas transmission rate results than the control Samples 13-14, which wereformed of commercially available thermoplastic urethane resins. Each ofthe samples, namely Samples 2-10 which relate to polyethylene glycoladipate and ethylene glycol glutarate based urethanes and Samples 11-12which relate to polyethylene glycol adipate based urethane blends,including BAREX™ 210, generally demonstrated better gas transmissionrate values than the polybutanediol adipate based urethane of Sample 1.As illustrated, each of the Samples 2-12, exhibited a gas transmissionrate of less than 15.0 for N₂ at 20 mils.

A multi-layer sample was also prepared by laminating two layers of thepolyester polyol based urethane as set forth in Sample 11 of Table Ialong with a third layer of commercially available material known asISOPLAST™. To laminate the multi-layer sample, a sheet of 5 milISOPLAST™ film was sandwiched between two layers of the polyester polyolbased urethane, each having a thickness of 19 mils. The multi-layersample was then pressed within a hydraulic press having upper and lowerplatens heated to about 420° F. The films were pressed together at apressure of about 2,000 psig to give rise to a sample having an overallthickness of approximately 18.25 mils.

Upon conducting the gas transmission rate analysis on the multi-layersample, it was discovered that the sample had a GTR of 8.87 for nitrogenat 18.25 mils and as normalized to 20.0 mils had a GTR of 8.09. Thus,the multi-layer sample also met the objective of a gas transmission rateof less than 15.0.

Finally, in addition to the monolayer and multi-layer membrane samplesas set forth above, a thermoset version of a polyester polyol basedurethane was also prepared and analyzed for gas transmission.

The sample, as set forth in Table III below, was prepared by dehydratingand degassing the polyester polyol under a vacuum for two hours at 100°C. and cooled to 60° C. at which time the catalyst was added.Concurrently, the Isonate™ 2143L was heated to 45° C. and degassed fortwenty minutes before its addition to the polyester component. Thepolyester polyol and polyisocyanate were then mixed and stirredcarefully in a polypropylene beaker to avoid the introduction of air.Upon mixing, the mixture was cast into a warm plaque mold where it wasallowed to cure for two hours at ambient temperature and pressure beforedemolding. The resulting membrane was allowed to remain at ambientconditions for seven days prior to testing.

TABLE III Ethylene glycol adipate 77.36 (a) 1000 m.w.¹ MDI² 22.34Catalyst³ 0.30 100.0 ¹FOMREZ ™ 22-225 available from Witco Chemical²ISONATE ™ 2143L which is a liquid MDI available from Dow Chemical Co.of Midland, MI. ³COCURE ™ 55 which is available from Caschem Inc., ofBayonne, N.J.

The thermoset version of the polyester polyol based urethanes as setforth in Table III exhibited a gas transmission rate of 3.07 for a 73mils thickness. Upon normalizing, the gas transmission rate wascalculated to be 11.2 for N₂ based on a 20 mil thickness. Thus, boththermoplastic and thermoset materials appear to be useful in accordancewith the teachings of the present invention.

In addition to the improved resistance to gas transmission offered bythe various products formed from the polyester polyol based urethanesdescribed herein, products made from polyester polyol based urethaneshave also shown a marked improvement in durability over thermoplasticurethanes which do not include polyester polyols.

For example, as illustrated in Table IV below, multiple samples wereprepared and analyzed for durability utilizing a test method known as asa KIM test. In accordance with the KIM test procedures, two sheets wereextruded from differing materials with each sheet being formed intoidentically shaped cushioning device components having an average wallthickness of 18 mils. The material utilized for the Set A cushioningdevices is the same as that set forth in Table I as Formulation No. 11.The Set B cushioning devices were made from a material such asPellethane 2355-85A, a thermoplastic urethane that does not contain anypolyethylene glycol adipate soft segments.

Upon inflating the cushioning devices to 20.0 psig with nitrogen gas,each sample was intermittently compressed by a reciprocating pistonhaving a 4.0 inch diameter platen. The stroke of each piston wascalibrated to travel a height which would compress each sample to anaverage of 25.0% of the initial inflated height at maximum stroke. Thereciprocating pistons were then allowed to cycle or stroke until a partfailure was detected. Part failure, as the term is used herein, isdefined as a sufficient leakage of the nitrogen gas and deflation of thecushioning device to cause a lever placed in identical locations alongeach of the cushioning devices to contact a microswitch which stops thereciprocating piston stroke. The total number of cycles or strokes werethen recorded for each sample with a high number of strokes beingindicative of a more durable material. Preferably, permanently inflatedcushioning devices should be capable of withstanding at least about200,000 cycles to be considered for applications as footwear components.

As can be seen from a review of Table IV, the cushioning devices of SetA formed from the polyester polyol based urethane outperformed thecushioning devices formed from the aromatic thermoplastic based urethaneof Set B by over three times as many cycles. Thus, the polyester polyolbased urethanes utilized under the present invention not only offerbetter resistance to undesired gas transmission, but also have beenshown to offer enhanced durability over thermoplastic urethanes which donot include polyester polyol soft segments having eight or less carbonatoms having eight or less carbon atoms in the repeating units.

TABLE IV Sample No. Avg No. of Cycles Set A* 754,111 Set B** 217,797*Average of 9 tests **Average of 10 tests

In addition to a high degree of durability, it is often desirable toform products which are relatively transparent in nature, i.e. productswhich meet certain standards in terms of the yellowness level detectedand the transmission of light through the material. For example,transparency of the product is often a consideration for cushioningdevices such as those utilized as components of footwear wherein thecushioning device is visually accessible.

In this regard, cushioning devices formed from Pellethane 2355-87ATP, anaromatic thermoplastic based urethane, have proven to be useful for shoecomponents since the material has been shown to offer acceptable levelsboth in terms of the yellowness level detected and the lighttransmission through the material. Thus, polyester polyol basedurethanes would preferably have similar and, more preferably, improvedtransparency characteristics as compared to aromatic thermoplasticurethanes such as Pellethane 2355-87ATP, among others.

Samples of both Pellethane 2355-87ATP and a polyester polyol basedurethane including: 50.96 wt. % FOMREZ 22-122 (1000 m.w.); 9.11 wt. %1,4 Butanediol; 38.81 wt. % ISONATE 2125M; 0.50 wt. % IRGANOX 1010; 0.15wt. % ADVAWAX 280; 0.30 wt. % montan ester wax; and 0.02 wt. % catalyst,were prepared by extruding smooth sided, collapsed tubes having anaverage wall thickness of 32 mils. Each sample was thereafter analyzedfor its yellowness index and the total transmission of lighttherethrough utilizing a Hunter Lab Color QUEST™ Spectocolorimeter inaccordance with the instrument's instruction manual.

The yellowness index readings were standardized in the {rsin} mode, andreadings were taken along the reflectance port. The total transmissionmeasurements were also standardized and the measurements were taken byreadings without glass slides along the transmission ports.

The Pellethane 2355-87ATP had a yellowness index of 4.00 and a totaltransmission of light of 90.85% based on a maximum value of 100.0%transmission. The polyester polyol based urethane had a yellowness indexof 1.52 and a total transmission of light of 91.75%. The polyesterpolyol based urethanes, thus, not only appear to be more durable thanaromatic thermoplastic based urethanes but also appear to offer bettervalues both in terms of a lower yellowness index and a higher lighttransmission. This improvement in terms of both decreased yellowness andan increased transmission of light should enhance the aestheticcharacteristics of many final products.

While the above detailed description describes the preferred embodimentof the present invention, it should be understood that the presentinvention is susceptible to modification, variation and alterationwithout deviating from the scope and fair meaning of the subjoinedclaims.

What is claimed is:
 1. A shoe, comprising a cushioning device; whereinsaid cushioning device comprises a sealed and inflated flexiblemembrane, said membrane comprising a polyurethane including a polyesterpolyol and said membrane having a gas transmission rate of about 15 orless for nitrogen gas.
 2. A shoe according to claim 1, wherein said shoeincludes an upper and a sole, and further wherein said sole includes thecushioning device.
 3. A shoe according to claim 1, wherein saidcushioning device is at least partially exposed to the atmosphere.
 4. Ashoe according to claim 3, wherein said cushioning device is part of anoutsole of said shoe.
 5. A shoe according to claim 1, wherein saidmembrane includes a thermoset material.
 6. A shoe according to claim 1,wherein said membrane is inflated with a gas to a pressure of greaterthan 0 psig.
 7. A shoe according to claim 1, wherein said membrane isinflated with a gas that comprises nitrogen.
 8. A shoe according toclaim 1, wherein said polyester polyol has repeating units comprisingeight or fewer carbon atoms.
 9. A shoe according to claim 1, whereinsaid polyester polyol is a reaction product of a dicarboxylic acidselected from the group consisting of adipic acid, glutaric acid,succinic acid, malonic acid, oxalic acid, and combinations thereof witha diol selected from the group consisting of ethylene glycol,propanediols, butanediols, pentanediols, hexanediols, and combinationsthereof.
 10. A shoe according to claim 1, wherein said polyurethane isthe reaction product of a combination comprising the polyester polyol, apolyisocyanate, and an extender.
 11. A shoe according to claim 10,wherein said extender comprises a member selected from the groupconsisting of ethylene glycol, propylene glycol, 1,4-butanediol,1,6-hexanediol, and combinations thereof.
 12. A shoe according to claim1, wherein said polyurethane comprises up to 30% by weight of saidpolyester polyol.
 13. A shoe according to claim 1, wherein said membranefurther comprises a barrier material selected from the group consistingof copolymers of ethylene and vinyl alcohol, polyvinylidene chloride,copolymers of acrylonitrile and methyl acrylate, polyethyleneterephthalate, polyamides, crystalline polymers, polyurethaneengineering thermoplastics, and combinations thereof.
 14. A shoeaccording to claim 13, wherein said membrane comprises at least about50% by weight of said barrier material.
 15. A shoe according to claim 1,wherein said membrane having a gas transmission rate of about 10 or lessfor nitrogen gas.
 16. A shoe according to claim 1, wherein said membranehaving a gas transmission rate of about 7.5 or less for nitrogen gas.17. A shoe according to claim 1, wherein said membrane is a multi-layerstructure having at least a first layer comprising said polyurethane anda second layer comprising a material selected from the group consistingof copolymers of ethylene and vinyl alcohol, polyvinylidene chloride,copolymers of acrylonitrile and methyl acrylate, polyethyleneterephthalate, polyamides, crystalline polymers, polyurethaneengineering thermoplastics, and combinations thereof.
 18. A shoeaccording to claim 17, wherein said second layer comprises a copolymerof ethylene and vinyl alcohol.
 19. A shoe, comprising a cushioningdevice; wherein said cushioning device comprises a sealed and inflatedflexible membrane, said membrane comprising a polyurethane including apolyester polyol and said membrane having a durability of at least200,000 cycles under a KIM test analysis.
 20. A shoe, comprising acushioning device; wherein said cushioning device comprises a sealed andinflated flexible membrane, said membrane comprising a polyurethaneincluding a polyester polyol and said membrane having a yellowness indexof 4.0 or less.